1. Field of the Invention
The present invention relates generally to the field of nonlinear optics. Specifically, it relates to the two-photon absorption measurement of materials.
2. Description of the Prior Art
In the past few years there have been many applications of two-photon absorption-fluorescence in the field of compact visible sources and microscopy. This rapidly developing field of research and development requires a large variety of materials of high two-photon absorption coefficient, fluorescence efficiency and environmental stability. The materials of particular importance are organic chromophore doped transparent polymeric materials and compound semiconductors.
Dependable measurement techniques exist for the real part of the third-order nonlinearity [such as Z-scan shown in FIG. 7 and THG etc.] in bulk materials. However, the dominant method for the measurement of two-photon absorption (TPA) coefficient (imaginary part of the third-order nonlinearity) in a material has been nonlinear transmission. In the bulk form, it is difficult and involved to experimentally consider nonlinear beam propagation effects, like self-focusing (defocusing) while measuring transmission at different intensities. To enable sufficient absorption for measurement, the concentrations of dye solutions are usually too high where aggregate formation masks the characterization of the monomeric species. In the thin film form, nonlinear waveguide transmission is used for the propagation of a high intensity beam over a long length of the medium. This technique is tedious in its sample preparation and coupling estimation besides the facet damage issues involved.
It is therefore a principal object of the invention to provide novel measurement of nonlinear optics absorption coefficients (second order and higher) of any semiconductor, organic and inorganic material in liquid or solid (bulk or thin film) form which is extremely sensitive and reliable due to being nearly background-free and without nonlinear beam propagation effects.
It is an additional object of the invention to provide a measurement system and method that requires no particular sample preparation, since the measurement can be done in liquid or solid (bulk or thin film) forms, in reflection or transmission mode.
It is another object of the invention to accommodate ultralow concentration (&lt;1 mM/L) required in doped materials, allowing characterization of monomeric species and not of aggregates which exists in the more highly concentrated solutions needed in conventional methods.
It is yet another object of the invention to provide a system and method that can easily be automated, computer controlled and integrated into commercially available spectrophotometers.
It is a further object of the invention to utilize tunable diode lasers, standard optics and detectors allowing a system to be packaged in a space of 0.5 meter by 1 meter.
These and other objects of the invention will become apparent as the detailed description of representative embodiments proceeds.